Method for build separation from a curing interface in an additive manufacturing process

ABSTRACT

A layer-by layer method for additive manufacturing that includes: photocuring a first volume of resin to form a layer of a build at an upper surface of a separation membrane laminated over a build window; injecting a fluid into an interstitial region between the separation membrane and the build window; retracting the build from the build window; evacuating the fluid from the interstitial region; and photocuring a second volume of liquid resin to form a subsequent layer of the build between an upper surface of a separation membrane and the previous layer of the build.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. Patent Application Ser. No. 16/672,410, filed on 1-Nov.-2019, which claims the benefit of U.S. Provisional Application No. 62/754,411, filed on 1-Nov.-2018, each of which is incorporated in its entirety by this reference.

This Application is a continuation of U.S. Patent Application Ser. No. 16/672,415, filed on 1-Nov.-2019, which claims the benefit of U.S. Provisional Application No. 62/754,430, filed on 1-Nov.-2018, which is incorporated in its entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the field of additive manufacturing and more specifically to a new and useful method for build separation in a digital light process in the field of additive manufacturing.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flowchart representation of a method.

FIGS. 2A and 2B are schematic representations of a system;

FIGS. 3A and 3B are schematic representations of the system;

FIGS. 4A and 4B are schematic representations of the system;

FIGS. 5A and 5B are schematic representations of the system;

FIG. 6 is a schematic representation of the system;

FIG. 7 is a schematic representation of the system;

FIG. 8 is a flowchart representation of the method;

FIG. 9 is a flowchart representation of the method;

FIG. 10 is a flowchart representation of the method;

FIG. 11 is a flowchart representation of the method; and

FIGS. 12A, 12B, and 12C are flowchart representations of the method.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is not intended to limit the invention to these embodiments but rather to enable a person skilled in the art to make and use this invention. Variations, configurations, implementations, example implementations, and examples described herein are optional and are not exclusive to the variations, configurations, implementations, example implementations, and examples they describe. The invention described herein can include any and all permutations of these variations, configurations, implementations, example implementations, and examples.

1. Method

As shown in FIG. 1, a method for additive manufacturing includes: photocuring a first volume of resin to form a first layer of a build at an upper surface of a separation membrane laminated over a build window, the first layer of the build adhering to a build platform in Block S110; injecting a fluid into an interstitial region between the separation membrane and the build window in Block S120; retracting the build platform from the separation membrane in Block S130; evacuating the fluid from the interstitial region to peel the separation membrane from the first layer of the build in Block S140; and photocuring a second volume of liquid resin to form a second layer of the build between the upper surface of the separation membrane and the first layer of the build in Block S150.

Also shown in FIG. 1, one variation of the method S100 includes: photocuring a first volume of resin to form a first layer of a build at an upper surface of a separation membrane laminated over a build window in Block S110; injecting a fluid into an interstitial region between the separation membrane and the build window in Block S120; retracting the first layer of the build from the build window in Block S130; evacuating the fluid from the interstitial region in Block S140; and photocuring a second volume of liquid resin to form a second layer of the build between an upper surface of a separation membrane and the first layer of the build in Block S150.

As shown in FIG. 11, one variation of the method S100 includes: photocuring a first volume of resin to form a first layer of a build at an upper surface of a separation membrane laminated over a build window, the first layer of the build adhering to a build platform in Block S110; injecting a fluid into an interstitial region between the separation membrane and the build window in Block S120; retracting the build platform from the separation membrane in Block S130; evacuating the fluid from the interstitial region to peel the separation membrane from the first layer of the build in Block S140; advancing the build platform toward the build window to a target position above the separation membrane laminated to the build window, the target position based on a layer thickness parameter of the build in Block S142; and photocuring a second volume of liquid resin to form a second layer of the build between the upper surface of the separation membrane and the first layer of the build in Block S150.

As shown in FIGS. 12A, 12B, and 12C, another variation of the method S100 includes: during a first photocuring phase, photocuring a first volume of liquid resin to form a first layer of a build between an upper surface of a separation membrane laminated to a build window and a build platform in Block S110; during a pressurization phase subsequent to the first photocuring phase, injecting a fluid into an interstitial region between the separation membrane and the build window in Block S120; during a retraction phase, retracting the build platform from the build window in Block S130; during a relamination phase subsequent to the pressurization phase, evacuating the fluid from the interstitial region to peel the separation membrane from the first layer of the build and laminate the separation membrane to the build window in Block S140; and, during a second photocuring phase subsequent to the relamination phase, photocuring a second volume of liquid resin to form a second layer of the build between an upper surface of a separation membrane and the first layer of the build in Block S150.

2. Applications

Generally, an additive manufacturing system 100 (hereinafter “the system 100”) executes the method S100 to selectively irradiate resin, via a stereolithographic process—such as a digital light process (hereinafter “DLP”) or a continuous digital light process (hereinafter “CDLP”)—to cure successive layers of a solid, physical object or set of objects (hereinafter “a build”). In a standard bottom-up stereolithographic additive manufacturing system, a layer of resin may tend to adhere (or “stick”) to the surface of a build window within this additive manufacturing system when photocured (e.g., via exposure to specific wavelength(s) of electromagnetic radiation); this layer of cured resin is then separated from this build window prior to advancement of a build platform (to which the build is adhered) and prior to introducing and photocuring a subsequent layer of resin. The resulting force from this separation can: deform the intermediate state of the ongoing build (in its “green” state) resulting in poor dimensional accuracy; increase the probability of build failure; and reduce print speeds, amongst other issues. The system 100 reduces these separation forces via inclusion of a replaceable separation membrane 160 (laminated over the upper surface of a build window 110 during a photocuring phase of a build process), which functions to limit adhesion forces (e.g., Stefan adhesion, suction forces) between newly cured layers of the build and the build window 110. Additionally, the system 100 includes a pressure regulation system 190 (e.g., a compressor/pump, and/or valve system) to selectively inject fluid (i.e. gases or liquids transmissive to electromagnetic radiation projected by a projection system 120) into an interstitial region between the build window 110 and the separation membrane 160 to obviate any need to directly separate a newly cured layer of the build from an inflexible build window during advancement of a build platform (as would be executed in a standard bottom-up stereolithographic process0.

In particular, the system 100 executes a build cycle to cure a new layer of a build; to separate the separation membrane 160 from the build window 110, and the newly cured layer of a build from the separation membrane 160; and to advance in preparation for curing a subsequent layer of the build. The build cycle includes: a photocuring phase (Block S110) to selectively photocure a layer of resin according to the cross-sectional geometry of the build; a pressurization phase (Block S110) to inject fluid into the interstitial region between the separation membrane 160 and the build window 110 thereby facilitating separation of the separation membrane 160 from the build window 110; a retraction phase (Block S130) to fully separate the separation membrane 160 from the build window 110 and to begin separating or fully separate the build (in its “green state”) from the separation membrane 160 by peeling (e.g., via a vector separation process) the separation membrane 160 away from the newly cured layer; and a relamination phase (Block S140) to evacuate fluid from the interstitial region thereby relaminating the separation membrane 160 against the build window 110 in preparation for photocuring a subsequent layer. Once the system 100 has executed a build cycle, the system 100 can execute a second photocuring phase (Block S150) to form the subsequent layer of the build. In one implementation, the method S100 can also include an advancement phase (Block S142), after the relamination phase, to reposition the build platform 106 and the adhered prior layers of the build in preparation for curing the subsequent layer of the build.

Thus, the system can execute the method S100 to distribute separation forces—between a photocured resin layer of a build and the separation membrane 160—evenly across the resin layer by increasing fluid pressure in an interstitial region between the separation membrane 160 and the build window 110 while retracting the build platform 106 away from the build window 110. By distributing separation forces across the photocured resin layer, the system may thus minimize peak forces at any one location across the photocured resin layer, thereby reducing opportunity for damage or deformation of this layer or previously photocured layers of the build. Additionally, the distribution of separation forces enables the use of resins exhibiting lower green strengths immediately after photocuring. Furthermore, by actively drawing the separation membrane 160 back down across the flat, rigid build window 110, and removing substantially all fluid therebetween, the system can: rapidly prepare the build volume for a subsequent resin layer; and consistently achieve a flat surface facing the build platform 106 and exhibiting high parallelism to the build platform 106. Therefore, the system can execute the method S100 to produce resin layers of consistent, controlled thickness and produce highly accurate builds with a high degree of repeatability across discrete builds and in less time.

Additionally, the system can execute the method S100 to achieve the foregoing results with minimal actuation of mechanical components, thereby increasing build speed, reducing system wear, and increasing repeatability across individual resin layers and across builds. Furthermore, the system can also include a tray assembly 104 configured to be engaged into and disengaged from a base assembly 102 (including the projection system 120, the build window 110, the build platform 106 etc.) and configured to repeatably locate the separation membrane 160 over the build window 110; a user can thus exchange tray assemblies containing separation membranes of different materials and/or thicknesses in order to match the separation membrane 160 to the particular chemical and physical properties of a photocurable resin selected for the next build and/or to the cross-sectional features or other geometric properties of the next build (e.g., thinner separation membranes for builds with small features). The tray assembly 104 can additionally or alternatively be disassembled to enable the user to exchange separation membranes matched to resin chemistries and/or build geometries for a build before rengaging the tray assembly 104 into the base assembly 102. Furthermore, because the method S100 does not exclusively rely on an oxygenated layer over the surface of the build window 110 or separation membrane 160 to achieve separation of a resin layer, the system can execute the method S100 to additively manufacture builds with resins that are oxygen-inhibited or not oxygen stable.

3. Hardware

As shown in FIG. 2A, the system 100 includes two subassemblies of electromechanical components that, when engaged in an engaged configuration, can execute a “bottom-up” DLP process. Generally, the system 100 includes a base assembly 102 and a tray assembly 104. A user may: assemble the tray assembly 104 by inserting a separation membrane 160 into the tray structure 150; and engage the tray assembly 104 with the base assembly 102 before the system 100 executes the method S100. The system 100 can then execute the method S100 via an imbedded computational device running computer code (hereinafter the “controller”), which electronically actuates the build platform 106 (e.g., via a linear actuation system) and controls the projection system 120 and the pressure regulation system 190 to selectively cure volumes of resin and to separate these cured volumes of resin from the build window 110 and separation membrane 160.

The system 100, in executing Blocks of the method S100, proceeds through multiple physical arrangements of the components in order to cure a build (e.g., a set of physical, 3D objects) from the resin contained within the tray assembly 104. In a lamination phase, the system 100 reduces the pressure (i.e. draws a vacuum/evacuates fluid from) in the interstitial layer between the separation membrane 160 and the build window 110, thereby fully laminating the separation membrane 160 against the build window 110 and preventing formation of bubbles or wrinkles that may disrupt the reference surface for the system 100. During the lamination phase, the system 100 can execute Block S110 of the method in order to photocure a selective volume of resin above the laminated surface of the separation membrane 160. Subsequent to completion of Block S110, the system 100 can execute a separation process including a pressurization phase, a retraction phase, and a relamination phase, corresponding to Blocks S120, S130, and S140 respectively. In the pressurization phase the system 100 injects fluid into the interstitial region, thereby generating separation between the separation membrane 160 and the build window 110 in order to reduce adhesion forces (e.g., Stefan adhesion, suction forces) between the newly cured layer of the build and the build window 110. In the retraction phase, the system 100 actuates the build platform 106 upward and away from the build window 110: to separate the separation membrane 160 from the build window 110; to peel the separation membrane 160 from the newly cured layer of the build; and to make space to photocure a successive layer of resin. In the relamination phase, the system 100 evacuates fluid from the interstitial region in order to peel the separation membrane 160 from the newly cured layer of the build and to relaminate the separation membrane 160 against the build window 110 in preparation for curing a successive layer of the build. Thus, the system 100 can repeat this process cycle to cure successive layers of the resin, thereby constructing a three-dimensional build.

3.1 Base Assembly

The system 100 includes a base assembly 102, which acts as the primary assembly resembling a 3D printer. The base assembly 102 includes a projection system 120, a window platform 132, a build window 110, a fluid distribution port 140 and/or a fluid distribution channel 142, a gasket system, a pressure regulation system 190, a tray seat 130, a build platform 106, and a controller. The base assembly 102 can be a free-standing structure that may be placed on a level surface for best printing results. The free-standing structure of the base assembly 102 links the aforementioned components in a calibrated arrangement that ensures consistent alignment between the projection system 120 and the build window 110 and parallelism between the reference plane of the build window 110, the surface of the retractable build platform 106, and the focal plane(s) of the projection system 120. The structure of the base assembly 102 can be manufactured from any rigid material that does not significantly deform under the weight of the base assembly 102 or the stresses involved during repetitive build cycles.

The base assembly 102 can also include a build chamber, into which the tray assembly 104 may be loaded (e.g., via engagement with the tray seat 130), and a hatch to provide access to this build chamber. The base assembly 102 can further include systems configured to control the environment within the build chamber (e.g., such as an auxiliary pressure regulation system 190 and/or a set of heating elements).

3.1.1 Projection System

The projection system 120 is upward facing, is housed in the base assembly 102, and can include one or more projectors configured to project electromagnetic radiation in an emissive spectrum, which can include the ultraviolet (hereinafter “UV”), visible, or near infrared (hereinafter “NIR”) spectrum. The projection system can emit electromagnetic radiation in one or more wavelength bands tuned to the chemical and physical properties of the resin and its specific curing process. For example, the projection system 120 (e.g., a digital UV projector) can project electromagnetic radiation in an emissive spectrum of 300-nanometer to 450-nanometers. The projection system 120 is electrically coupled to the controller; receives potentially software-modified frames corresponding to full or partial cross-sections of a three-dimensional model of the build; and projects electromagnetic radiation through the build window 110 and separation membrane 160 in the engaged configuration (and during the photocuring phase) to selectively photocure volumes of the resin according to build settings and the received frames.

In one variation, the system 100 can include a projection system 120, which further includes a set of light sources, such as projectors or other electromagnetic emitting devices. In this variation, each irradiation source of the projection system 120 can define a projective area within the build window 110 in order to maintain a higher resolution across the build window 110 via tiling or stitching techniques. Additionally or alternatively, each light source can define a separate emissive spectrum enabling the projection system 120 to project electromagnetic radiation within multiple combinations of spectral bands.

In one variation, the projection system 120 includes a UV or near-UV laser and scans (e.g., as a raster) a laser beam across the build window 110 according to frames received from the controller in order to selectively photocure a volume of resin located over the separation membrane 160.

3.1.2 Window Platform

Generally, the window platform 132 extends upwards from a tray seat 130 of the base assembly 102 and is configured to align within a tray aperture 152 of the tray assembly 104 when the system 100 is in the engaged configuration. The window platform 132 is a rigid structure that encompasses the projection system 120 and defines an opening above the upward facing projection system 120 that is spanned by the build window 110. The upper surface of the window platform 132 defines a horizontal reference plane which is coincident with the upper surface of the build window 110 and the primary focal plane of the projection system 120. The system 100 can include a window platform 132 of a shape that: corresponds to a shape of a tray aperture 152; enables engagement with the separation membrane 160; and is configured to define fluid distribution ports 140 and/or fluid distribution channels 142 around the build window 110 and within the interstitial region. For example, the upper surface of the window platform 132 can define a circular shape, a rectangular shape, or any other shape depending on the desired shape of the tray aperture 152. In an additional example, the system 100 can include a window platform 132 of any size larger than the build region of the system 100 and/or the dimensions of builds to be manufactured by the system 100. The system 100 can include a window platform 132 with filleted corners and edges around the upper surface of the window platform 132 to prevent tearing of the separation membrane 160 as it is tensioned over the window platform 132.

The window platform 132 defines an opening that is spanned or partially spanned by the build window 110. Generally, the shape and size of the opening defined by the window platform 132 roughly corresponds with the shape and size of the upper surface of the build window 110 in order to maximize utilization of the build region of the system 100.

3.1.3 Build Window

The build window 110 is mounted to the window platform 132 such that the upper surface of the build window 110 is approximately flush with the upper surface of the window platform 132 and further defines the horizontal reference plane for builds manufactured in the system 100. The build window 110 is arranged above the projection system 120 and aligned with the projection area of the projection system 120 such that the focal plane of the projection system 120 coincides with the upper surface of the separation membrane 160 laminated over the build window 110. Generally, the build window 110 is substantially transparent (e.g., exhibiting greater than 85% transmittance) to the emissive spectrum of the projection system and thus passes electromagnetic radiation output by the projection system 120 into the resin above the build window 110 and separation membrane 160. The build window 110 also functions as a rigid support and reference surface for the separation membrane 160 and a layer of resin arranged thereover. The build window 110 is statically mounted to a base assembly 102, via the window platform 132, that can include the projection system 120, the build platform 106, the fluid distribution port 140, the pressure regulation system 190, and/or the build chamber to ensure repeatable, accurate alignment between the build window 110 and the rest of the base assembly 102. The interface between the rigid window platform 132 and the build window 110 is also gas-impermeable such that a pressure gradient, such as 300 kilopascals, can be sustained across the build window 110.

The base assembly 102 can include a build window 110 manufactured from a pane of transparent, rigid glass, such as amorphous/silicate or crystalline/ceramic glass. In particular, the build window 110 can be both transparent to ultraviolet (or other) light output by the projection system 120 and can be substantially rigid, hard, and temperature-stable to form a robust, flat reference surface that supports the separation membrane 160 and that may exhibit minimal deflection or deformation during multiple build cycles, thereby yielding high and consistent build quality.

In one variation, the base assembly 102 can include a build window 110 that is transmissive to infrared (hereinafter “IR”) radiation such that a thermographic sensor positioned below the build window 110 can accurately calculate the temperature of the resin during a during the photocuring phase of the build cycle.

3.1.4 Fluid Distribution Ports

The base assembly 102 includes one or more fluid distribution ports 140 configured to fluidically (i.e. pneumatically or hydraulically) couple the pressure regulation system 190 to the interstitial region between the separation membrane 160 and the build window 110, thereby enabling the pressure regulation system 190 to inject and/or evacuate fluid from the interstitial region while the system 100 is in the engaged configuration. The fluid distribution ports 140 can therefore be located within a gasket system that forms a seal between the base assembly 102 and the tray assembly 104 and, more specifically, between the build window 110 and the separation membrane 160. Each fluid distribution port 140 can define an opening that is fluidically coupled to the pressure distribution system 100 to enable the system 100 to adjust the pressure within the interstitial region via the pressure distribution port by injecting and/or evacuating fluid from the fluid distribution ports 140. In one implementation, the system 100 includes an inlet fluid distribution port 140 and an outlet fluid distribution port 140, which provides an inlet for fluid entering the interstitial region and an outlet for fluid evacuating from the interstitial region respectively. Alternatively, the base assembly 102 includes a single fluid distribution port 140, which is configured with the pressure regulation system 190 as both an outlet and an inlet for fluid in the interstitial region. In another implementation, the base assembly 102 can include additional fluid distribution ports 140 arranged throughout the interstitial region in order to reduce asymmetrical fluid flow from one side of the interstitial region to another.

3.1.5 Fluid Distribution Channel

In one variation, the base assembly 102 includes a fluid distribution channel 142 intersecting the fluid distribution ports 140 and configured to distribute fluid evenly throughout the interstitial region. More specifically, the base assembly 102 can include a fluid distribution channel 142 configured to reduce asymmetrical fluid flow relative to the build window 110 and the separation membrane 160 by distributing fluid from a fluid distribution port 140 throughout the interstitial region. Thus, when fluid is injected into or evacuated from the interstitial region, the entire region is pressurized and/or depressurized substantially simultaneously, thereby preventing bubble formation in the separation membrane 160 or uneven separation of the separation membrane 160 from the build during the retraction and/or relamination phase.

In one implementation, the fluid distribution channel 142 is integrated within the window platform 132 supporting the build window 110 and defines a channel inset into the upper surface of the rigid window platform 132. In this implementation, the fluid distribution channel 142 is arranged circumferentially around the perimeter of the build window 110 and intersects an inlet fluid distribution port 140 and an outlet fluid distribution port 140 fluidly coupled to the pressure regulation system 190. Thus, the base assembly 102 can include a fluid distribution channel 142 circumscribing the build window 110 and configured to distribute fluid evenly in the interstitial region.

However, the base assembly 102 can include a fluid distribution channel 142 defining any path throughout the interstitial region that reduces asymmetrical fluid flow within the interstitial region.

3.1.6 Pressure Regulation System and Pressure Chambers

Generally, as shown in FIG. 7, the base assembly 102 can include a pressure regulation system 190 configured to pressurize and/or depressurize by injecting and/or evacuating fluid from the interstitial region in accordance with the method S100. More specifically, the base assembly 102 can include a pressure regulation system 190 that is: fluidically coupled to the fluid distribution port 140; configured to inject fluid into the interstitial region to separate the separation membrane 160 from the build window 110 in the engaged configuration and during a pressurization phase; and configured to evacuate fluid from the interstitial region to laminate the separation membrane 160 to the build window 110 in the engaged configuration and during a lamination phase.

The pressure regulation system 190 can include a pump (e.g., a diaphragm pump) and a set of electromechanical valves connected by a set of tubes to the fluid distribution ports 140. More specifically, the pressure regulation system 190 can include a pump fluidically coupled to a set of two electromechanical valves configured to actuate in response to commands from the system 100 and direct fluid flow through the pump into the interstitial region or out of the interstitial region based on a current phase of the build cycle.

In one implementation, the pressure regulation system 190 includes a set of electronically actuated valves configured to regulate flow between a compressed fluid supply line (e.g., a compressed air supply line in the building housing the system) and a central vacuum line. The system 100 can, therefore, be connected—such as via external ports—to the compressed fluid supply line and the central vacuum line.

In another implementation, the pressure regulation system 190 includes a compressor system 100 (e.g., a centrifugal compressor) and an external air port and is configured to: intake ambient air via the external air port; compress this ambient air; and inject this ambient air into the interstitial region. The pressure regulation system 190 can also evacuate air from the interstitial region via the compressor and the external air port by running the compressor system 100 in reverse. Alternatively, the pressure regulation system 190 is fluidly coupled to a fluid reservoir (e.g., a tank containing an inert fluid). Thus, the system 100 can inject fluid from the fluid reservoir into the interstitial region or evacuate this fluid into the fluid reservoir via the pressure regulation system 190.

In yet another implementation, the base assembly 102 can include a compressor system 100 and/or a system 100 of electronically actuated valves configured to draw fluid from the pressurized build chamber (e.g., above the surface of the resin reservoir contained in the build tray) in order to pressurize the interstitial region in the pressurization phase. Likewise, the system 100 can evacuate fluid from the interstitial region back into the build chamber during the relamination phase and/or the lamination phase. Thus, in this implementation, the system 100 can operate independently from external sources of a working fluid for pressurization or depressurization of the interstitial region.

Additionally or alternatively, the base assembly 102 can include a second pressure regulation system 190 configured to control the pressure of the build chamber independent from the pressure of the interstitial region. The system 100 can coordinate the first pressure regulation system 190 and the second pressure regulation system 190 to improve separation (e.g., reduce separation forces and increase separation speed) of the separation membrane 160 from the cured resin layer of the build.

The pressure regulation system 190 can maintain a maximum operating inflation differential pressure up to or exceeding 300 kilopascals and can pull a vacuum (e.g., a maximum operating deflation pressure) greater than 200 kilopascals. These pressures are sufficient to adequately separate the separation membrane 160 from the build window 110 in the pressurization phase and to laminate the separation membrane 160 to the build window 110 in the lamination and/or the lamination phase. However, the pressure regulation system 190 can maintain alternative operating differential pressures based on the volume of the interstitial region and the force exerted on the interstitial region by the separation membrane 160 due to the particular elasticity and thickness of the separation membrane 160.

Additionally, the pressure regulation system 190 can include resin traps and can be configured to purge these resin traps (via the actuation of purge valves) to remove resin from these resin traps when the pressure regulation system 190 is accidentally contaminated with resin (e.g., due to spillage from the resin reservoir during engagement or failure of the separation membrane 160 due to excessive wear). Alternatively, the pressure regulation system 190 can purge resin from the fluid distribution ports 140 by pumping fluid out of the fluid distribution ports 140 while the base assembly 102 is disengaged from the tray assembly 104.

3.1.7 Gas-Permeable Layer

Generally, as shown in FIG. 6, the base assembly 102 can include an intermediate gas-permeable layer 180 arranged over the surface of the build window 110 and between the build window 110 and the separation membrane 160 when the system 100 is in the engaged configuration. More specifically, the base assembly 102 can include a gas-permeable layer 180 that is: substantially transparent to electromagnetic radiation within the photo-initiating range; arranged over the upper surface of the build window 110; and configured to maintain a minimum interstitial volume within the interstitial region between the build window 110 and the separation membrane 160 in the engaged configuration. Thus, by maintaining space between the separation membrane 160 and the build window 110 in the engaged configuration, the gas-permeable layer 180 reduces the incidence of bubbles between the separation membrane 160 and the build window 110 during the lamination phase of the build cycle. Additionally, inclusion of the gas-permeable layer 180 can reduce or eliminate suction forces between the separation membrane 160 and the build window 110.

In one implementation, the base assembly 102 includes a gas-permeable layer 180 that defines a gas-permeable grid or lattice structure over the build window 110. In this implementation, the gas-permeable layer 180 can be manufactured from a material that is substantially transparent (e.g., greater than 85% transmittance) and characterized by the similar index of refraction as the build window 110 in order to reduce aberrations in the projection incident with the resin opposite the separation membrane 160 during the photocuring process.

3.1.8 Tray Seat

The base assembly 102 can define a tray seat 130 around the base of the window platform 132 with a surface offset below the upper surface of the window platform 132 such that the window platform 132 protrudes upwards from the center of the tray seat 130. The tray seat 130 defines a surface with a high degree of parallelism with the reference plane defined by the window platform 132. Additionally, the vertical offset between the tray seat 130 and the reference plane can be calibrated and/or constructed with a low tolerance such that, when the tray assembly 104 is seated at the tray seat 130 of the base assembly 102 in the engaged configuration, the separation membrane 160 is precisely positioned relative to the build window 110. In one variation, the system 100 includes a tray seat 130 and tray assembly 104 tolerance stack that positions the separation membrane 160 slightly above (e.g., less than 1 millimeter above) the build window 110 when there is no pressure gradient across the separation membrane 160. In another variation, the system 100 defines a tray seat 130 and tray assembly 104 tolerance stack that positions the upper surface of the window platform 132 and/or build window 110 such that these surfaces protrude into the tensioned separation membrane 160 while the system 100 is in the engaged configuration, thereby automatically laminating the separation membrane 160 against the build window 110.

The tray assembly 104 can define a set of registration features 154 corresponding to complimentary reference features 134 arranged on the tray seat 130 of the base assembly 102. Therefore, in the engaged configuration, the registration features 154 can constrain the tray assembly 104 relative to the base assembly 102. In one implementation, the reference features 134 of the base assembly 102 and the registration features 154 of the tray assembly 104 are configured to kinematically align the tray assembly 104 relative to the base assembly, thereby maintaining a precise offset between the separation membrane 160 and the build window 110 and/or preventing movement of the tray assembly 104 relative to the base assembly 102 during the build cycle. In another implementation, the base assembly 102 can include imbedded magnetic features underneath the tray seat 130 in order to bias the tray assembly 104 downward onto the reference features 134 of the tray seat 130. Alternatively, the base assembly 102 can include a set of mechanical clamps or screws in order to seat the tray assembly 104 at the tray seat 130 of the base assembly 102.

3.1.9 Reference Features

Generally, the reference features 134 defined by the tray seat 130 are configured to correspond to matching features in the tray assembly 104 and to thus align the tray assembly 104 with the base assembly 102. More specifically, the base assembly 102 can define positive reference features 134 or negative reference features 134 on the tray seat 130. Alternatively, the base assembly 102 can include reference features 134 that are separate components configured to install onto the tray seat 130. In combination with a biasing force, such as a magnetic force between corresponding magnetic features in the base assembly 102 and tray assembly 104, mechanically applied force securing the tray assembly 104 to the base assembly 102, and/or the force of gravity pulling the tray assembly 104 downward onto the base assembly 102, the reference features 134 kinematically constrain the tray assembly 104 relative to the base assembly 102 in all six degrees-of-freedom. Thus, corresponding reference features 134 defined in the tray seat 130 and in the tray assembly 104 can repeatably and accurately align the tray assembly 104 with the base assembly 102 when the tray assembly 104 is engaged with the base assembly 102.

3.1.10 Magnetic Locking Mechanism

Generally, the system 100 can include a set of magnets imbedded within the base assembly 102 below the tray seat 130 and a corresponding magnetic material (e.g., a ferromagnetic substance) imbedded within the tray assembly 104, thereby biasing the tray assembly 104 toward the tray seat 130. More specifically, the base assembly 102 can include a magnetic lock arranged within the tray seat 130; and the tray assembly 104 can include a magnetic registration feature 154 configured to magnetically engage with the magnetic lock in the engaged configuration.

In one implementation, the base assembly 102 can include an electromagnetic lock as the magnetic lock such that the system 100 can actively engage and/or disengage the tray assembly 104 from the base assembly 102 via an electrical current. Thus, the base assembly 102 can include an electromagnetic lock configured to: magnetically engage with the magnetic registration feature 154 in the engaged configuration; and magnetically disengage with the magnetic registration feature 154 in a disengaged configuration.

3.1.11 Build Platform

Generally, the base assembly 102 also includes a vertically mobile build platform 106 to which a first layer of the build adheres and from which the build is suspended toward the build window 110 during the build cycle. More specifically, the base assembly 102 can include a build platform 106 defining a planar surface opposite and substantially parallel to the upper surface of the build window 110; and a linear actuation system (including a single linear actuator or multiple timed linear actuators) configured to vertically translate the build platform 106 relative to the build window 110. In one implementation, the system 100 can include a build platform 106 defining negative features, such as channels or through holes to improve the flow of resin out from under the build platform 106 during advancement of the build platform 106 into the resin reservoir and to facilitate the removal of the build from the build platform 106 after completion of the build.

The build platform 106 is a vertically actuating surface opposite the build window 110. The system 100 can include a linear actuation system (with increments as small as 0.1 microns) mechanically coupled to the build platform 106. Additionally, during actuation of the linear actuation system, the controller: can track forces applied by the linear actuation system to the build platform 106 (e.g., based on a current draw of the linear actuation system or by sampling a force sensor or strain gauge coupled to the build platform 106); and implement closed-loop techniques to control movement of the linear actuation system in order to achieve a particular distribution of separation forces between the newly cured layer of the build and the separation membrane 160 (e.g., to sweep this separation force along a predefined force profile once per layer). Thus, during the build cycle the linear actuation system lowers the build platform 106 to specific heights above the separation membrane 160 such that photocured resin adheres to the build surface of the build platform 106 facing the window. As the system 100 selectively cures successive layers of the build according to Blocks of the method S100, the system 100 can retract the build platform 106 upward by a first distance in order to separate the current layer of the build from the separation membrane 160 and then advance the build platform 106 downward—by a second distance less than or equal to the first distance—in preparation for curing a successive layer of the build.

3.1.12 Controller

The base assembly 102 of the system 100 can include a controller that controls the electromechanical components of the system 100. Generally, the controller is an imbedded computer system that sends instructions to the projection system 120, the pressure regulation system 190, and the linear actuation system coupled to the build platform 106, to execute the method S100. In one implementation, the controller controls and receives instructions from a user interface, which can be a touchscreen or a set of buttons, switches, nobs, etc. Alternatively, the controller can communicate with and receive instructions from an external computational device. In another implementation, the controller is connected to a network, such as the internet, and is configured to receive instructions over the network. Additionally, the controller can send commands, in the form of digital and/or analog electrical signals, in order to actuate various electromechanical components of the system such as the magnetic locking mechanism, a door hatch release to the build chamber, the purge valves, and/or lighting elements within the build chamber. Furthermore, the controller can receive data from sensors integrated with the system 100 and execute feedback control algorithms based on these data in order to modify the function of the projection system 120, the pressure regulation system 190, and/or the linear actuation system.

3.2 Tray Assembly

As shown in FIG. 2B, the system 100 includes a tray assembly 104 (i.e. a build tray) which further includes: a tray structure 150 (which can define an upper member 155 and a lower member 156), a separation membrane 160, a set of tensioning gaskets 162, and/or a resin-sealing gasket 164. The tray assembly 104 is configured to engage (e.g., kinematically mount to) the base assembly 102 over the window platform 132 via corresponding registration features 154 arranged on the underside of the tray structure 150 and reference features 134 on the tray seat 130. Generally, the tray assembly 104 contains the resin reservoir during a build cycle and positions and maintains the tension in the separation membrane 160 over the window platform 132, build window 110, and/or fluid distribution ports 140. More specifically, the tray assembly 104 can include a tray structure 150 that defines an upper member 155 and a lower member 156, which are fastened together via a set of fasteners with the separation membrane 160 in between the upper member 155 and the lower member 156. Thus, the tray structure 150 functions to position the separation membrane 160 so that it is configured to: laminate across the upper surface of the build window 110 in response to an evacuation of fluid, via the fluid distribution port 140, from an interstitial region between the base assembly 102 and the tray assembly 104 in the engaged configuration; and configured to separate from the build window 110 in response to injection of fluid, via the fluid distribution port 140, into the interstitial region.

In one implementation, the base assembly 102 includes a sealed build chamber that encloses the tray assembly 104 and sealed. Additionally, the build chamber can be filled with an inert fluid, such as to enable use of reactive (e.g., reactive with oxygen) resin chemistries in the system 100. In one implementation, the build chamber is integrated with the upper member 155 of the tray structure 150. In this implementation, the resin can be injected into the inner volume of the assembly including the build tray and the build chamber via an injection port such that the resin is not exposed to the atmosphere at any point while being loaded into the tray assembly 104.

3.2.1 Tray Structure

Generally, the tray structure 150: defines a tray aperture 152 spanned by the separation membrane 160 and circumscribing the build window 110; defines registration features 154 configured to engage with the reference features 134 of the tray seat 130; and defines an interior volume for containing the resin reservoir. The tray structure 150 can be constructed from a rigid, non-reactive, temperature stable solid material, such as aluminum or another metal or metal alloy. In one implementation, the tray structure 150 is constructed from milled aluminum. Additionally, the tray assembly 104 can be a member of a set of tray assemblies associated with the system 100, each tray assembly 104 in the set of tray assemblies including a tray structure 150 of a different shape or size in order to accommodate a wider variety of build sizes and shapes. In one implementation, the tray structure 150 includes an upper member 155 and a lower member 156 configured to fasten to each other via a set of fasteners. Thus, during assembly of the tray assembly, a user may arrange the separation membrane 160 between the lower member 156 and the upper member 155, thereby repeatably locating the separation membrane 160 relative to the tray seat 130 in the engaged configuration.

Generally, the upper member 155 of the build tray defines the volume occupied by the resin during the build cycle and the region within which the system 100 can selectively photocure this resin into the build via execution of a series of build cycles. The upper member 155 also defines an tray aperture 152 that corresponds to the window platform 132 such that the upper member 155 can be lowered over the window platform 132 of the base assembly 102. The tray aperture 152 in the upper member 155 is spanned by the separation membrane 160 thereby enclosing the volume defined by the upper member 155 from the bottom. Thus, the tray assembly 104 when fully assembled defines an interior volume above the separation membrane 160 tensioned across the tray aperture 152, the interior volume configured to contain a reservoir of resin.

In one implementation, an inner surface of the build region is rounded to reduce stress concentrations in the separation membrane 160. In one implementation, the upper member 155 of the build tray defines a rounded rectangular build region. Additionally, the upper member 155 can define an inner surface that extends upward and perpendicular to the build window 110. The inner surface then expands upward and outward in a conical shape, wherein the vertical cross section of the conical inner surface has dimensions proportionally similar to the vertical cross-section of the perpendicular inner surface. Thus, the perpendicular and conical sections of the inner surface define a volume configured to contain the resin reservoir. However, the upper member 155 of the build tray can define any rounded internal volume. Additionally, the upper member 155 can include integrated heating and/or cooling elements. The system 100 can activate the heating and/or cooling elements to adjust the temperature of the resin within the build tray to near an optimal temperature for the photocuring reaction of the resin.

The lower member 156 defines a shape consistent with the inner surface of the upper member 155 and can define corresponding features to the reference features 134 in the tray seat 130 of the base assembly 102. In one implementation, the base assembly 102 and/or the lower member 156 contain magnets (i.e. magnetic registration features 154), which kinematically align the lower member 156, and therefore the tray assembly 104, to the base assembly 102 by biasing the lower member 156 against the reference features 134 in the base assembly 102. The lower member 156 also defines holes such that fasteners, such as screws or bolts, passing through the holes can insert into corresponding holes in the upper member 155. Alternatively, the system can include fasteners that are directly integrated with either the upper member 155 and/or the lower member 156 and the system can include an upper member 155 and a lower member 156 configured to slot directly into the opposite member of the tray structure 150.

3.2.2 Separation Membrane

The separation membrane 160 can include a transparent, thin, and flexible film or sheet characterized by low adhesion to photocuring resins. The separation membrane 160 is manufactured at sizes specific to particular tray assemblies 104 and with holes aligned with tensioning posts 159 extending from either the upper member 155 or the lower member 156 of the build tray. Thus, the separation membrane 160 is positioned between the upper member 155 and the lower member 156 of the build tray such that the tensioning posts 159 extend from one member of the tray structure 150, through a hole, slot, or perforation in the separation membrane 160, and into corresponding negative features in the opposite member of the tray structure 150. Additionally or alternatively, the separation membrane 160 can define a set of holes and/or slots such that there is an interference fit between the separation membrane 160 and the set of tensioning posts 159, thereby preloading (i.e. automatically tensioning) the separation membrane 160 with a tensile stress.

Thus, the tray assembly 104 can include an upper member 155 and a lower member 156 with interlocking features and a separation membrane 160 perforated in an interference fit with these interlocking features. Therefore, the geometry of the tensioning posts 159 relative to the corresponding perforations in the separation membrane 160 functions to automatically tension the separation membrane 160 across the tray aperture 152 defined by the tray structure 150. For example, the upper member 155 of the tray structure 150 can define milled positive features including the tensioning posts 159 corresponding to milled negative features in the lower member 156 such that the negative features of the lower member 156 fit over the positive features of the upper member 155. In this example, the separation membrane 160 defines perforations corresponding to the positive features of the upper member 155 in an interference fit. In this implementation, the tray assembly 104 can further include separate fasteners—such as magnets, clasps, latches, and/or screws—to fasten the lower member 156 to the upper member 155.

However, the separation membrane 160 can be tensioned across the tray aperture 152 defined by the tray structure 150 in any other way (e.g., via direct bonding to the tray structure 150 or via another fastening configuration).

Thus, in one implementation, the tray assembly 104 can include: an upper member 155 defining a set of positive features including a set of tensioning posts 159; a lower member 156 defining a set of negative features configured to engage with the set of positive features; a separation membrane 160 arranged between the upper member 155 and the lower member 156 and defining a third set of perforations outwardly offset from the set of tensioning posts in an interference fit between the separation membrane 160 and the set of tensioning posts 159 tensioning the separation membrane 160 via the interference fit.

3.2.3 Separation Membrane Selection

As described above, the system 100 can include an interchangeable separation membrane 160. Therefore, a user may select different tray assemblies containing various separation membranes and tray structure configurations and/or install separation membranes of different types in one tray assembly 104 based on various factors, such as: the geometry (e.g., feature sizes) of a build queued for manufacture by the system 100; characteristics of the resin chemistry selected for the build and a corresponding photocuring process; the target green strength of the selected resin; and/or cumulative wear or degradation of the separation membrane 160. The separation membrane 160 is replaceable by removing the fasteners in the tray assembly 104 and separating the upper member 155 and the lower member 156 of the build tray from the separation membrane 160. After the separation membrane 160 is removed a new separation membrane 160 can be placed over the tensioning posts 159, thereby securing the new separation membrane 160 between the upper member 155 and the lower member 156 of the build tray.

Because the separation membrane 160 is exchangeable within the build tray, the system 100 can include multiple types of separation membranes with varying sizes, thicknesses, tensions, permeabilities, elasticities and/or materials, which may be selected by a user or specified by the system 100 based on the resin loaded into the interchangeable tray assembly 104. In one implementation, the separation membrane 160 is constructed from copolymerized tetrafluoroethylene (hereinafter “TFE”) and has a thickness less than one millimeter, and low fluid permeability. Alternatively, the membrane is constructed from 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (hereinafter “TFE-AF”) and has high oxygen permeability such that a layer of the resin can be oxygenated.

In one implementation, the system 100 includes an oxygen-permeable separation membrane 160 to allow oxygen to saturate a layer above the separation membrane 160 within the resin. In resins with oxygen-inhibited chemistries, the oxygen saturated layer can therefore prevent the resin from photocuring against (and adhering to) the separation membrane 160 or the build window 110 to a certain depth beyond the separation membrane 160. In this implementation, the separation membrane 160 can be constructed from TFE-AF. Additionally, the system 100 can include a separation membrane 160 of a greater thickness and/or stiffness, an increased offset between the separation membrane 160 and the build window 110, and/or execute a decreased peak inflation pressure during Block S120 (e.g., so that the separation can diffuse oxygen into the resin without substantially deflecting). In one implementation, the pressure applied to the interstitial region between the build window 110 and the separation membrane 160 is matched to the atmospheric pressure at the upper surface of the separation membrane 160 such that the pressure gradient across the separation membrane 160 is negligible.

When the system 100 is manufacturing a build with relatively delicate features, a thinner membrane (e.g., between 20 microns and 50 microns thick) can be inserted into the tray assembly 104. The thinner membrane may have greater elasticity and therefore may impart a smaller magnitude of force as it is pulled away from the layer features during each build cycle. However, thinner separation membranes 160 may wear more rapidly (e.g., over fewer build cycles) than thicker separation membranes and thus may require replacement at a higher frequency. Conversely, a thicker separation membrane 160 (e.g., up to 150 microns thick) may be loaded into the tray assembly 104 when builds defining more robust geometries are queued at the system 100, since a thicker separation membrane 160 may be more resistant to cumulative wear, may be replaced less often, and may withstand greater forces necessary to separate larger resin features from the build window 110. For example, a user may load a thin separation membrane 160 into the build tray when a resin with low green strength is selected for a next build in the system 100, since this thinner separation membrane 160 may apply lower forces to layers of this cured resin. However, the user may also load a thicker separation membrane 160 into the build tray when a resin with higher green strength is selected for a next build in the system 100, since this thicker separation membrane 160 may be more robust and/or may be inflated faster than a thin separation membrane 160, thereby enabling shorter separation periods between layers of the build. Thus, a first tray assembly 104 can include a first separation membrane 160 defining a first thickness between 50 and 200 microns and a second tray assembly 104 can include: the tray structure 150 of the first tray assembly 104; and a second separation membrane 160, defining a thickness less than 50 microns, tensioned across the tray aperture 152 defined by the tray structure 150, configured to configured to laminate across the upper surface of the build window 110 in response to an evacuation of fluid, via the fluid distribution port 140, from an interstitial region between the base assembly 102 and the tray assembly 104 in the engaged configuration, and configured to separate from the build window 110 in response to injection of fluid, via the fluid distribution port 140, into the interstitial region.

Additionally, the user may exchange separation membranes 160 according to the chemistry of the resin or the photocuring reaction of the resin in order to improve release characteristics of the resin. Although TFE is generally chemically stable, separation membranes 160 of alternative compositions can be included in the system 100 when manufacturing with an especially reactive resin composition or resins that exhibit especially exothermic photocuring reactions. In alternative implementations, tray assembly 104 can include a separation membrane 160 manufactured from semi-crystalline perfluoroalkoxy alkane (i.e. PFA) or fluorinated ethylene propylene (i.e. FEP). In one implementation, the separation membrane 160 is coated with a transparent super-hydrophobic nanocoating to prevent adhesion between the separation membrane 160 and the build in its green state.

Furthermore, the system 100 can be supplied with a set of separation membranes 160 characterized by different oxygen or gas permeabilities. For example, a separation membrane 160 of TFE or PFA may be relatively impermeable to oxygen (e.g., at thicknesses greater than 50 microns) and therefore may be loaded into the tray assembly 104 when the system 100 is photocuring an oxygen-sensitive resin such as a thiol resin or a polyolefin resin. Thus, the tray assembly 104 can include a separation membrane 160 manufactured from an oxygen-impermeable film. Because the system 100 can control the oxygen concentration in the resin reservoir (via an inert environment in the build chamber and an oxygen-impermeable membrane), the system 100 can photocure resins containing lower proportions of photoinitiator, thereby improving photocuring speed, cross-link density, and green strength of builds constructed from these resins.

Alternatively, the user may load a separation membrane 160 of TFE-AF into the build tray in order to intentionally create an oxygen rich region in the resin reservoir to inhibit photocuring of the resin proximal to the separation membrane 160, thereby further improving separation from the separation membrane 160 at the expense of limiting the variety of resin chemistries that are compatible with the separation membrane 160. Thus, the tray assembly 104 can include a separation membrane 160 manufactured from a gas-permeable film.

The tray assembly 104 can further include a separation membrane 160 characterized by a high heat deflection, continuous use, or glass transition temperature, thereby enabling the separation membrane 160 to resist higher reaction temperatures (e.g., up to 100 degrees Celsius) typical of certain resin chemistries. Thus, the tray assembly 104 can include a separation membrane 160: characterized by a heat deflection temperature greater than 100 degrees Celsius; and chemically inert to the resin at a temperature of less than 100 degrees Celsius. However, the system can include a separation membranes 160 characterized by heat deflection temperature less than the reaction temperature of the photocurable resin at the expense of an increased rate of wear.

3.2.4 Tensioning Gaskets

In one implementation, the upper member 155 and the lower member 156 include a set of rubber or rubberized plastic gaskets arranged around each tensioning post 159 to distribute tensile force applied to the separation membrane 160 over a larger area, thereby preventing excessive lateral movement/shifting or tearing of the separation membrane 160 while under tension. The tensioning gaskets 162 effectively sandwich the separation membrane 160 to bear the load of the tension in the membrane across the entire area of the gasket. In addition, the tray assembly 104 can include tensioning gaskets 120 configured to achieve a particular distribution (e.g., an even distribution) of tensile forces across the membrane and a particular inflationary profile or behavior of the separation membrane 160 (e.g., similar separation of the membrane independent of location within the build region).Thus, the tensioning gaskets 162 can be arranged on the bottom surface of the upper member 155 and/or the upper surface of the lower member 156 around the holes defined for the tensioning posts 159 in the upper member 155 and the lower member 156.

3.2.5 Resin-Sealing Gasket

The system 100 can also include a resin-sealing gasket 164 arranged along the edge of the tray aperture 152 of the upper member 155 of the build tray. Generally, the resin-sealing gasket 164 prevents resin ingress between the upper member 155 of the build tray and the separation membrane 160. Thus, when the tray assembly 104 is lowered over and around the window platform 132, the separation membrane 160 is tensioned and pulled upward by the window platform 132 protruding through the inner opening of the build tray spanned by the separation membrane 160. The separation membrane 160 is thus biased against the resin-sealing gasket 164 on the edge of the interior opening of the upper member 155 of the build tray creating a seal against resin held in the build tray. Additionally, the resin-sealing gasket 164 can prevent excess shear stress from tearing the separation membrane 160 when it comes into contact with the interior edge of the upper member 155 of the build tray.

In implementations where the separation membrane 160 is not pulled upward by a protruding window platform 132 in the engaged configuration (e.g., in implementations where the separation membrane 160 is positioned less than one millimeter above the build window 110 in the engaged configuration when there is no pressure gradient across the separation membrane 160), the tray assembly 104 can include a set of resin-sealing gaskets 164 circumscribing the tray aperture 152 in between the separation membrane 160 and the upper member 155 of the tray structure 150.

3.3 Inter-Assembly Gasket Configurations

Generally, the system 100 can define an inter-assembly gasket configuration in order to fluidically isolate (e.g., for a maximum operating pressure such as 300 kilopascals) the interstitial region from the build chamber and from external ambient environment in order to enable precise control of the pressure within the interstitial region via the pressure regulation system 190. Because the interstitial region is enclosed during engagement of the tray assembly 104 with the base assembly 102, the inter-assembly gasket configuration can include gaskets integrated with the tray assembly 104, the base assembly 102, and/or independent gasket components therebetween.

3.3.1 Active Lamination Gasket Variation

In an active lamination gasket variation, shown in FIGS. 4A and 4B, the system 100 includes a gasket integrated with the lower member 156 of the tray assembly 104 circumscribing the bottom edge of the tray aperture 152 defined by the lower member 156 of the tray assembly 104 and configured to seal (i.e. within the maximum operating pressure of the system) against the base of the window platform 132 and/or the tray seat 130 in the engaged configuration. Additionally, as shown in FIG. 4A, when the system 100 is in the engaged configuration and while there is no pressure gradient across the separation membrane 160, the separation membrane 160 is suspended by the tray structure 150 offset from (by greater than 50 microns) and parallel the surface of the build window 110. Thus, when the pressure regulation system 190 evacuates fluid from the interstitial region (and, therefore, induces a negative pressure gradient across the separation membrane 160) the separation membrane 160 laminates against the upper surface of the build window 110 as shown in FIG. 4B. More specifically, the system 100 can include an interface gasket 172: arranged between a lower surface of the tray structure 150 and a base of a window platform 132 supporting the build window 110 in the engaged configuration; circumscribing the tray aperture 152, the fluid distribution port 140, and the build window 110 in the engaged configuration; and configured to seal fluid within the interstitial region up to a maximum differential pressure greater than a maximum operating pressure. Additionally, in this implementation, the system 100 includes a tray assembly 104 which further includes the separation membrane 160 tensioned across the tray aperture 152 above and substantially parallel to the build window 110 in the engaged configuration.

In the active lamination gasket variant, the positioning of the separation membrane 160 offset (e.g., by greater than 50 microns) above the build window 110 reduces the incidence of bubble formation between the separation membrane 160 and the build window 110 during the relamination phase because, as the system 100 pulls a vacuum across the separation membrane 160 during the relamination phase, the volume of the interstitial region decreases pulling to separation membrane 160 toward the build window 110 from the center of the membrane. Therefore, the separation membrane 160 laminates against the build window 110 from the center outwards, thereby preventing bubble formation during this relamination.

Additionally, in this variation, the base assembly 102 can include one or more fluid distribution ports 140 that are arranged anywhere within the tray assembly 104 and the base assembly 102. In one implementation, the fluid distribution port 140 is arranged on the base of the window platform 132, thereby facilitating the even distribution of air around the window platform 132.

In one implementation, the tray assembly 104 can include a sealing gasket arranged between the lower member 156 of the tray structure 150 and the separation membrane 160 and circumscribing the tray aperture 152 defined by the lower member 156 in order to prevent egress of fluid from the interstitial region during the pressurization phase of the build cycle.

3.3.2 Passive Lamination Gasket Variation

In a passive lamination gasket variation, shown in FIGS. 5A and 5B, the system 100 includes an interstitial gasket 170 circumscribing the edge of the window platform 132, which is configured to protrude through the tray aperture 152 defined by the tray assembly 104 such that the separation membrane 160 is tensioned over the surface of the window platform 132 and creates a seal with the interstitial gasket 170 in the engaged configuration. Therefore, in this variation, the system 100 defines an interstitial region that includes only the volume of fluid between the separation membrane 160 and the build window 110 (as opposed to also including fluid between the tray assembly 104 and the base assembly 102). Additionally, in this variation, the system 100 can include a fluid distribution port 140 arranged on the surface of the window platform 132 proximal to the build window 110, thereby enabling the pressure regulation system 190 to inject and/or evacuate fluid from this more localized interstitial region, as shown in FIG. 5B. As shown in FIG. 5A, the separation membrane 160 is laminated across the build window 110 without a negative pressure gradient between the interstitial region and the build chamber. Alternatively, in this variation, the system 100 can include a fluid distribution port 140 inset into the window platform proximal to a raised build window defining an upper surface coincident with the edge of the window.

More specifically, the base assembly 102 can include the build window 110 configured to protrude through the tray aperture 152 against the separation membrane 160 in the engaged configuration. Additionally, the base assembly 102 can include an interstitial gasket 170: circumscribing the fluid distribution port 140 and the build window 110; configured to contact the separation membrane 160 in the engaged configuration; and configured to seal fluid within the interstitial region up to a maximum differential pressure greater than a maximum operating pressure.

The interstitial gasket 170 can be manufactured from rubber or rubberized plastic that can form a seal with the tensioned separation membrane 160. Like the upper surface of the build window 110, the upper surface of the interstitial gasket 170 is flush with the upper surface of the window platform 132 and is coincident with the horizontal reference plane defined by the window platform 132. In one implementation, the interstitial gasket 170 can form a seal with the tensioned separation membrane 160, when the tray assembly 104 is engaged with the base assembly 102, that can withstand a pressure gradient of 300 kilopascals.

In one implementation of this passive lamination variation, the system 100 can include a window platform 132, which is configured to protrude through the tray aperture 152 defined by the tray assembly 104 such that the separation membrane 160 is tensioned over the surface of the window platform 132 and creates a seal directly with the edge of the window platform 132 in the engaged configuration. This implementation obviates the need for the interstitial gasket 170 on the edge by creating a direct seal against the material of the window platform 132.

4. Engagement and Initialization

As shown in FIG. 2B, before the system 100 executes the method S100, the user may fasten the separation membrane 160 between the lower member 156 and upper member 155. Once the separation membrane 160 is fastened between the upper member 155 and lower member 156 of the build tray, the user may lower the tray assembly 104 over the upper surface of the window platform 132 and the build window 110. As shown in FIGS. 3A and 3B, the tray then kinematically aligns with the reference features 134 of the base assembly 102, thereby engaging with the base assembly 102. In the passive lamination variation, when the tray assembly 104 and the base assembly 102 are engaged the separation membrane 160 is tensioned flush against the surface of the build window 110 and covers the fluid distribution channel 142. In this variation, the separation membrane 160 also forms a fluid-impermeable seal (within the maximum operating pressure of the system) against an interstitial gasket 170 arranged along the edge of the window platform 132 or with the edge of the window platform 132 itself. In the active lamination gasket variation of the system, the separation membrane 160 is positioned just above the build window 110 upon kinematic alignment of the tray assembly 104 with the tray seat 130 of the base assembly 102.

Before or after the tray assembly 104 is engaged with the base assembly 102, resin is loaded into the volume defined by the upper member 155 of the build tray and the separation membrane 160. If the resin is not sensitive to oxygen and/or ambient air, the resin may be poured directly into the build tray. However, if the resin is sensitive to oxygen, humidity, and/or ambient air, the resin can be injected into a tray assembly 104 through a sealed port in a sealed build chamber after the build chamber has been filled with an inert fluid.

Thus, after loading is complete, the build volume defined by the inner surface of the build tray is at least partially occupied by a volume of resin. The resin is in contact with the upper surface of the separation membrane 160 and the inner surface of the upper member of the tray assembly 104. However, the resin does not come into contact with the build window 110 underneath the separation membrane 160.

5. Build Cycle

Generally, as shown in FIG. 1 and referenced above, the system 100 executes Blocks S110, S120, S130, and S140, to: selectively photocure a volume of resin corresponding to a layer of a build; separate the separation membrane 160 from the build window 110, and also the newly cured layer of the build from the separation membrane 160; and reposition the separation membrane 160 and build platform 106 (adhered to the first layer) in preparation for photocuring a subsequent layer. More specifically, the system 100: cures a first layer of the build; inflates the interstitial region between the separation membrane 160 and the build window 110; retracts (e.g., raises) the build platform 106 vertically upward away from the build window 110; and depressurizes the region between the separation membrane 160 and the build window 110 in order to peel the separation membrane 160 away from the first layer of the build and draw the separation membrane 160 down onto and flat against the build window 110. In one implementation, the system 100 can also advance/reposition the build platform 106 (and the adhered first layer of the build) such that the lower surface of the most recently cured layer of the build is offset from the surface of the separation membrane 160 (that is laminated across the build window 110) by a distance equal to a desired layer thickness of the next layer as shown in Block S142.

Additionally, as is further described below, the system 100 can execute Blocks S120, S130, S140 and/or S142 in a synchronized sequence—such as during discrete or (partially-) overlapping time periods—in order to repeatably separate build, including the newly cured layer of the build from the separation membrane 160 and with minimal damage or deformation of the build in its green state.

Furthermore, some Blocks of the method S100 may be described with reference to a “first layer” of the build. However any of the Blocks of the method S100 are also applicable to subsequent layers of the build.

5.1 Build Chamber and Resin Reservoir Conditions

In one implementation, prior to executing Block S110, the system 100 can adjust the temperature and pressure of the gas within the build chamber, and/or adjust the temperature of the resin in the resin reservoir.

For example, the system 100 can heat the resin in the reservoir (e.g., via heating elements integrated with the tray structure 150 or under the build window 110) in order to decrease the viscosity of the resin or cause a phase change in the resin from solid to liquid, thereby improving print speeds and printability of the resin. More specifically, the system 100 can access a target temperature for the resin based on a temperature-viscosity curve corresponding to the resin and a target viscosity for the resin; and heat the resin to the target temperature.

In another example, the system 100 can increase the temperature of the gas environment within the build chamber to match the target temperature for the resin in order to prevent convective currents from forming within the build chamber and therefore increasing evaporation rates of chemical components of the resin (which may degrade the performance of the resin). The system 100 can also heat the gas environment within the build chamber to prevent solidifying of resin surrounding a build in its green state after being retracted out of a heated resin bath, in implementations where the system maintains the resin in a liquid phase due to the elevated temperature of the resin reservoir. Additionally, the system 100 can control the temperature of the build chamber to prevent deformation of the build in its green state when exposed to differential pressures between the resin reservoir and the gas environment within the build chamber.

Furthermore, the system 100 can increase the pressure within the build chamber to reduce the evaporation rate of chemical components of the resin. In yet another example, the system 100 can introduce an inert fluid environment within the build chamber when the system 100 is photocuring especially reactive resin chemistries (e.g., oxygen-sensitive resin chemistries).

5.2 Lamination

As shown in FIG. 8, while selectively curing a current layer of resin in Block S110, the system 100 minimizes the interstitial space between the build window 110 and the separation membrane 160 in order to repeatably maximize flatness and planarity of the outer surface of the separation membrane 160 in Block S102. In one implementation, prior to executing Block S110, the controller can trigger the pressure regulation system 190 to draw a vacuum on this interstitial region in order to flatten the separation membrane 160 across the build window 110. The pressure regulation system 190 can also continue to draw vacuum on the interstitial space between the build window 110 and the separation membrane 160—via the fluid distribution port 140—in order to maintain contact between the build window 110 and the separation membrane 160 during Block S110. By drawing vacuum on this interstitial space prior to Block S110, the system 100 can thus remove bubbles from between the build window 110 and the separation membrane 160 and ensure that the separation membrane 160 is laminated flush against the surface of the build window 110. Thus, the system 100 can: concurrently draw a vacuum in the interstitial region to maintain lamination of the separation membrane 160 to the build window 110 while photocuring the first volume of liquid resin in Block S110; and concurrently draw a vacuum in the interstitial region to maintain lamination of the separation membrane 160 to the build window 110 while photocuring the second volume of liquid resin in Block S150.

Alternatively, the system 100 can achieve lamination via engagement between the tray assembly 104 and the base assembly 102, as described above and shown in FIGS. 5A and 5B. Thus, the system 100 can: photocure the first volume of resin to form the first layer of the build at the upper surface of the separation membrane 160 laminated over the build window 110 via engagement of a tray assembly 104 around the window platform 132, the separation membrane 160 tensioned over the build window 110 by the tray assembly 104 in Block S110; and photocure the second volume of resin to form the second layer of the build at the upper surface of the separation membrane 160 laminated over the build window 110 via engagement of the tray assembly 104 around the window platform 132, the separation membrane 160 tensioned over the build window 110 by the tray assembly 104 in Block S150.

5.3 Initial Photocuring Phase

In Block S110, the system 100 selectively photocures a first volume of resin to form a first layer of a build (e.g., corresponding to a first cross section of the build), wherein the build adheres to the build platform 106 opposite the separation membrane 160. Generally, once the build platform 106 has lowered into the resin at a height above the separation membrane 160 based on a desired layer thickness of the first layer of the build 160, the controller instructs the projection system 120 to irradiate selective areas of the resin between the separation membrane 160 and the build platform 106 corresponding to a first layer of the build. The resin is configured to photocure upon exposure to the emissive spectrum of the projection system 120. More specifically, the system 100 can: photocure the first volume of resin to form the first layer of the build above the upper surface of the separation membrane 160 laminated over the build window 110, the first layer of the build adhering to a build platform 106; and retract the build platform 106 and the first layer of the build from the separation membrane 160. Thus, upon selective irradiation, the resin photocures, thereby strongly adhering to the build platform 106 and minimally adhering to the separation membrane 160. Additionally, the separation membrane 160 may adhere to the build window 110 proximal to photocured features of the first layer due to adhesion forces (e.g., suction forces, Stefan adhesion) between the separation membrane 160 and the build window 110.

However, the system 100 can selectively photocure a volume of resin between the build platform 106 and the separation membrane 160 utilizing any stereolithographic, DLP, or directed radiation technique.

5.4 Pressurization Phase

Following photocuring of the first layer of the build in Block S110, the system 100 can execute Block S120, which includes triggering the pressure regulation system 190 to inject a fluid (e.g., air, oxygen, an inert gas) into the interstitial region between the build window 110 and the separation membrane 160 via the fluid distribution port 140. When the interstitial region is thus pressurized, the separation membrane 160 may begin to expand and to delaminate from the surface build window 110, such as from the perimeter of the build window 110 toward features of the current layer of the build that were cured in Block S110 (hereinafter “layer features”). The separation membrane 160 may thus exert a distributed circumferential “prying” force around the perimeter of each region of layer features in the newly cured layer of the build. For example, the pressure regulation system 190 can pressurize the interstitial region up to a pressure of 300 pascals, which may overcome adhesion forces (e.g., suction forces, Stefan adhesion) between the build window 110 and the separation membrane 160.

In one implementation, the pressure regulation system 190 injects an inert fluid into the interstitial region such that any fluid permeating the separation membrane 160 does not inhibit photocuring of the resin. Alternatively, the system 100 includes a separation membrane 160 constructed from TFE-AF or another oxygen-permeable material and the pressure regulation system 190 displaces oxygen (or oxygen-rich fluid) into the interstitial region such that an oxygenated layer forms across the outer surface of the separation membrane 160 when inflated in Block S120, thereby further preventing adhesion between the separation membrane 160 and layer features of the current layer of the build. In yet another alternative implementation, the system 100 can also include a separation membrane 160 that is substantially impermeable to oxygen (e.g., separation membrane 160 manufactured from crystalline PFA and characterized by a thickness greater than 50 microns). Thus, the system 100 can inject a fluid (e.g., such as air or an inert gas) into the interstitial region between the separation membrane 160 and the build window 110, where the separation membrane 160 is characterized by low gas permeability.

In another implementation, the system 100 does not actively inject fluid into the interstitial region while executing Block S120 and instead releases the vacuum being held during execution of Block S110 allowing the interstitial region to passively inflate.

As shown in FIG. 9, the system 100 can set a target interstitial pressure (e.g., a target absolute pressure or a target differential pressure relative to the build chamber) in the interstitial region in Block S120 and control the pressure regulation system 190 to reach this pressure within the interstitial region. In one implementation, the system 100 can set a target pressure corresponding to a target separation distance between the separation membrane 160 and the build window 110 resulting from the target interstitial pressure. In this implementation, an operator of the system 100 can empirically determine the target interstitial pressure that corresponds to a desired target separation distance. Alternatively, the system 100 can: evaluate a physical model of the separation membrane 160 and interstitial region to calculate a separation distance resulting from a range of interstitial pressures; and select a target interstitial pressure that results in the target separation distance.

Furthermore, because the separation distance resulting from interstitial pressure additionally depends on the weight of the resin in the resin reservoir and the ambient pressure within the build chamber, the system 100 can measure these variables prior to calculating the target interstitial pressure. For example, the system 100 can measure depth and volume of the resin by including a visible light camera positioned within the build chamber in order to record images of the resin reservoir. The system 100 can then execute computer vision techniques to calculate a volume of resin within the resin reservoir. Alternatively, system 100 can utilize a liquid level sensor to measure the depth and calculate the volume of the resin. Additionally, the system 100 can measure the temperature of the resin and access the density of the resin at the measured temperature in order to measure the total mass of the resin in the resin reservoir. The system 100 can then incorporate the mass of the resin in the reservoir as a variable in the physical model (or the empirical data) for the separation distance achieved by a range of interstitial pressures. Thus, the system 100 can: measure a mass of the resin over the separation membrane 160; calculate a target interstitial pressure based on a mass of resin in the reservoir, the target interstitial pressure corresponding to a target separation distance; and pressurize the interstitial region to the target interstitial pressure.

In another implementation, the system 100 can maintain the target interstitial pressure, during the pressurization phase, by executing a feedback control algorithm based on a current interstitial pressure. More specifically, the system 100 can: measure a series of interstitial pressures during the pressurization phase; and execute proportional-integral-derivative (hereinafter “PID”) control to pressurize the interstitial region to the target interstitial pressure.

In yet another implementation, the system 100 can measure the separation distance of the separation membrane 160 from the build window 110 and execute a PID control algorithm to modulate the interstitial pressure, during the pressurization phase, in order to achieve a target separation distance. More specifically, the system 100 can: measure a separation distance of the separation membrane 160 from the build window 110 during pressurization of the interstitial region; and adjust the target interstitial pressure based on the separation distance (e.g., via a PID control algorithm). In this implementation, the system 100 can include a laser distance meter configured to measure the separation distance. Additionally, the system 100 can access a separation distance profile and control this separation distance in accordance with the profile over time via a feedback control loop and input from the laser distance meter.

However, the system 100 can pressurize the interstitial region to a target interstitial pressure in any other way.

5.4.1 Selective Inflation

In one implementation, the system 100 can determine whether to exclude Block S120 (e.g., based on the geometry of the build or the resin material) from selective build cycles. The system 100 can exclude inflating the interstitial region between the build window 110 and the separation membrane 160 when the system 100 photocures a build layer with geometry (e.g., low cross sectional area) and material properties (e.g., high target green strength or low viscosity), such that it does not cause significant adhesion forces (e.g., suction forces, Stefan adhesion) between the separation membrane 160 and the build window 110. In this implementation, the system 100 does not execute Block S120 and begins executing Block S130 after the completion of Block S110. Furthermore, in this implementation, the system 100 can also exclude the relamination phase of Block S140 (e.g., for the passive lamination variation of the system 100).

5.4.2 Chemistry-Specific Gas Permeability

In one implementation, the system 100 includes an oxygen permeable separation membrane 160 to allow oxygen to saturate a layer above the separation membrane 160 within the resin for resins with oxygen-inhibited chemistries. The oxygen saturated layer can, therefore, prevent these resins from photocuring against and adhering to the separation membrane 160 within a certain depth beyond the separation membrane 160. In this implementation, the separation membrane 160 can be constructed from TFE-AF. Additionally, the system 100 can include a separation membrane 160 of a greater thickness and/or stiffness, an increased offset between the separation membrane 160 and the build window 110, and/or execute a decreased peak inflation pressure during Block S120 (e.g., so that the separation can diffuse oxygen into the resin without substantially deflecting). In one implementation, the pressure applied to the interstitial region between the build window 110 and the separation membrane 160 is matched to the atmospheric pressure at the upper surface of the separation membrane 160 such that the pressure gradient across the separation membrane 160 is negligible.

5.5 Retraction Phase

Generally, in Block S130, the build platform 106 retracts vertically upward away from the build window 110. More specifically, the controller instructs the linear actuation system coupled to the build platform 106 to exert an upward force in order to separate the build from the build window 110 and move the build upward. In one implementation, the system 100 applies, via the linear actuation system, force over time according to a material specific force profile consistent with the green strength and geometry of the build, as well as print conditions such as resin temperature and viscosity. When the sum of the upward force exerted by the build platform 106 and the prying force of the fluid inflating the interstitial space between the separation membrane 160 and the build window 110 is sufficient to overcome the adhesion forces (e.g., suction forces, Stefan adhesion) holding the separation membrane 160 proximal to the layer features of the build against the build window 110, the separation membrane 160 may separate from the build window 110 and begin moving upward with the build platform 106. However, the separation membrane 160 may still adhere to the build as it rises upward.

The system 100 can detect the instant at which the separation membrane 160 separates from the build window 110 (e.g., by measuring a change in the force applied by the linear actuation system coupled to the build platform 106) and can continue to actuate the build platform 106 upward in order to separate the separation membrane 160 from the build. As the build platform 106 actuates away from the build window 110, the separation membrane 160 may continue to stretch while adhered to the rising build. However, the rising build platform 106 increases the force angle between the bottom surface of the build and the separation membrane 160, which may cause the separation membrane 160 to peel away from the build.

In one implementation, as shown in FIG. 10, the system 100 can include a load cell within the build platform 106 to measure the cumulative force being applied to the build platform 106 and therefore the layer(s) of the build in its green state adhered to the build platform 106. Thus, the system 100 can measure the force exerted on the build platform 106 and/or the adhered build during the retraction phase via a load cell integrated with the build platform 106. Alternatively, the system 100 can estimate the force applied to the build platform 106 based on the torque of a motor configured to actuate the linear actuation system. In this implementation, the system 100 can execute closed-loop control algorithms—such as a PID control algorithm—to ensure that the peak force applied to the build platform 106 during the retraction phase does not exceed a maximum retraction force. The system 100 can calculate a maximum retraction force based on the green strength of the cured resin and/or the geometry of the build. For example, the system 100 can: access the geometry of the build (e.g., during the particular build cycle); estimate the distribution of force through this geometry over a range of applied forces (e.g., at the build platform 106) to identify a maximum stress and/or strain on the build; and estimate a maximum retraction force (as measured at the build platform 106) to prevent build failure based on the maximum stress and/or strain on the build and the green strength and/or geometry of the build. Thus, the system 100 can: access a maximum retraction force corresponding to the resin; measure a retraction force applied to the build platform 106 during retraction of the build platform 106; and adjust an acceleration and/or velocity of the build platform 106 based on the retraction force. The system 100 can also limit overshoot in the desired force profile applied to the build over multiple build cycles during Block S130, thereby improving build quality and consistency.

Additionally, upon separation of the first layer of the build from the build window 110, the system 100 can actuate the build platform 106 according to a displacement curve, which defines the displacement (and therefore the velocity and acceleration) of the build platform 106 as it translates upward through the resin reservoir. The system 100 can define a displacement curve that ensures stability of the build while in its green state as it moves through the (often viscous) resin within the resin reservoir and/or during the first stages of separation of the separation membrane 160 from the build window 110. Therefore, the system 100 can adjust the velocity and/or acceleration defined by the displacement curve based on the viscosity of the resin. For example, the system 100 can define a displacement curve characterized by a relatively high peak velocity and a relatively high peak acceleration for a resin characterized by a relatively low viscosity. In another example, the system 100 can define a displacement curve characterized by a relatively low peak velocity and a relatively low peak acceleration for a resin characterized by a relatively high viscosity. Thus, the system 100 can: define a displacement curve for the build platform 106 based on a target green strength of the resin and a viscosity of the resin; and retract the build platform 106 according to the displacement curve.

5.6 Relamination Phase

Generally, in Block S140, the pressure regulation system 190 evacuates fluid from (e.g., depressurizes) the interstitial region, thereby pulling the separation membrane 160 taught across the surface of the build window 110. Additionally, by pulling the separation membrane 160 downward toward the build window 110, the system 100 can increase the rate of separation between the separation membrane 160 and the build and/or reduce the total retraction distance needed to peel the separation membrane 160 away from the build. Furthermore, by depressurizing the interstitial region between the separation region and the build window 110, the system 100 ensures that the separation membrane 160 is laminated against the build window 110 such that there are no bubbles or wrinkles in the separation membrane 160 before the system 100 photocures a second layer in Block S150. More specifically, the system 100 can, via the pressure regulation system 190, reduce the differential pressure within the interstitial region relative to the build chamber in order to generate a downward force on the separation membrane 160 that causes the separation membrane 160 to separate from the newly cured layer of the build, if the separation membrane 160 has not already separated from the newly cured layer of the build due to retraction of the build platform 106 in Block S120. Furthermore, by reducing the differential pressure across the separation membrane 160, the system 100 can also increase the angle of separation of the separation membrane 160 from the build, thereby increasing the rate at which the separation membrane 160 may peel away from the newly cured layer of the build.

In one implementation, the system 100 can further decrease the differential pressure between the build chamber and the interstitial region by concurrently increasing the absolute pressure in the build chamber while decreasing the absolute pressure in the interstitial region. Thus, the system 100 can: pressurize a build chamber above the separation membrane 160 while evacuating the fluid from the interstitial region in order to further increase the force across the separation membrane 160 and improve separation of the separation membrane 160 from the newly cured layer of the build. By increasing the absolute pressure within the build chamber, the system 100 can also hasten the flow of resin underneath the retracted build platform 106 and adhered build in addition to increasing the force across the separation membrane 160.

5.7 Advancement Phase

In one implementation, as shown in FIG. 11, the system 100 executes an advancement phase by actuating the build platform 106 and adhered build via the linear actuation system to a distance relative to the separation membrane 160 such that the bottom surface of the build is a distance above the upper surface of the separation membrane 160 approximately equal to the desired layer thickness of the subsequent layer of the build in Block S142, or at or above a distance above the separation membrane 160 in preparation for the subsequent photocuring phase of Block S150. The system 100 can execute an advancement phase in implementations where the system 100 retracts the build platform 106 farther than the layer thickness of the build in order to improve the angle of separation of the separation membrane 160 against the bottom surface of the build. Thus, by increasing the retraction distance, the system 100 can increase this separation angle and therefore more effectively peel the separation membrane 160 away from the newly cured layer of the build. However, before photocuring a subsequent layer, the system 100 can advance the build (downward and toward the build window 110) such that the newly cured layer is offset from the surface of the separation membrane 160 (that is laminated to the build window 110) by the preset layer thickness for the build—enabling the system 100 to photocure a subsequent layer between the current layer and the upper surface of the separation membrane 160. More specifically, the system 100 can: advance the build platform 106 toward the build window 110 to a target position above the separation membrane 160 laminated to the build window 110, the target position based on a layer thickness parameter of the build; and photocure the second volume of resin to form the second layer of the build between the upper surface of the separation membrane 160 and the first layer of the build. In one implementation, further described below the system 100 can advance the build platform 106 to the same vertical position of the previous layer in order to cure a different selective volume of the same layer in the subsequent photocuring phase of Block S150. Additionally or alternatively, the system 100 can advance the build platform 160 to a vertical position enabling the system 100 to photocure a layer that overlaps with the previous layer in order to generate interlocking structures.

Additionally or alternatively, also shown in FIG. 11, the system 100 can execute an advancement delay between the relamination of the separation membrane 160 in the relamination phase and the advancement phase in order to allow the resin to settle in preparation for photocuring a subsequent layer. Furthermore, the system 100 can access (from an empirical data table) or calculate an advancement delay sufficient to allow the resin to flow back into position underneath the build and build platform 106. Thus, the system 100 can prevent translational flow in the resin reservoir caused by movement of the build platform 106 and the adhered build from affecting the features of the build during advancement of the build platform 106 in the resin reservoir prior to photocuring a subsequent layer of the build. More specifically, the system 100 can: access an advancement delay corresponding to the viscosity of the resin; and, during the advancement phase delayed from the relamination phase by the advancement delay, advance the build platform 106 toward the build window 110 to the target position above the separation membrane 160 laminated to the build window 110, the target position based on the layer thickness parameter of the build.

In another implementation, the system 100 can set an advancement speed and/or acceleration for the build platform 106 as it advances into or within the resin during the advancement phase. The system 100 can access (from an empirical data table) or calculate an advancement speed based on the distance of the build from the build window 110, the viscosity of the resin, the green strength of the resin, and/or the geometry of the build. For example, the system 100 can estimate the forces that may be imparted by the resin on the build upon insertion of the build into the resin reservoir over a range of advancement speeds. The system 100 can then select an advancement speed that the system 100 predicts will result in forces imparted to the build that are less than a threshold force. More specifically, the system 100 can: access a target advancement speed based on a viscosity of the resin and a geometry of the first layer of the build; and advance the build platform 106 toward the target position at the target advancement speed. Alternatively, the system 100 can: access an advancement profile specifying vertical positions of the build platform 106 over time; and actuate the linear actuation system according to this advancement profile during execution of Block S140 (e.g., according to feedback control algorithms), thereby enabling modulation of the advancement speed and/or acceleration over time.

5.7.1 Timing Variations

Generally, the system 100 executes Blocks S120, S130, and S140, in sequence as described above. However, as shown in FIGS. 12A, 12B, and 12C, the system 100 can execute Block S120 and S130 and/or Blocks S130 and S140 in an overlapping manner, thereby increasing build speeds. Additionally or alternatively, the system 100 can execute pauses between any Block of the method S100 to improve print conditions during any Block. In one implementation, shown in FIG. 12A, the pressurization phase and the retraction phase can overlap, enabling faster separation between the build and the build window 110. For example, the pressurization phase can begin and, as the system 100 approaches the target interstitial pressure, the system 100 can begin to retract the build platform 106 in the retraction phase. More specifically, the system 100 can, during the retraction phase concurrent with the pressurization phase, retract the build platform 106 from the build window 110.

In another implementation, shown in FIG. 12B, the system 100 can begin the relamination phase while the system 100 is still retracting the build platform 106 such that the separation membrane 160 can peel away from the build at a higher rate and relaminate to the build window 110 more quickly. In one example, the system 100 can forgo an advancement delay by initiating the relamination phase while the build platform 106 is still retracting providing time for the resin to flow underneath the build platform 106 as the build platform 106 moves upward. More specifically, the system 100 can, during the relamination phase concurrent with the retraction phase, evacuate the fluid from the interstitial region to peel the separation membrane 160 from the first layer of the build and laminate the separation membrane 160 to the build window 110.

In yet another implementation, shown in FIG. 12C, the system 100 can overlap the pressurization phase and the retraction phase and the retraction phase and the relamination phase, thereby further reducing the duration of the build cycle. Additionally or alternatively, the system 100 can modulate the interstitial pressure and the retraction speed in coordination with the overlapping phases. For example, the system 100 can detect separation of the newly cured layer from the build window 110 (e.g., based on force and/or acceleration detected at the build platform 106) and, in response to separation of the newly cured layer from the build window 110, begin evacuating fluid from the interstitial region. In another example, the system 100 can increase a retraction speed of the build platform 106 while concurrently initiating the relamination phase in order to more effectively peel the separation membrane 160 from the newly cured layer of the build.

5.7.2 Successive Photocuring Phases

Upon execution of Blocks S120, S130, S140, and/or S142, the system 100 executes Block S150 to photocure a second layer of the build. Once the build platform 106 and adhered build are at a target offset from the surface of the separation membrane 160, the system 100 can selectively photocure a second volume of the resin between a surface of the layer features of the previously photocured layer and the upper surface of the separation membrane 160 corresponding to a second cross-section of the build in order to connect this second cross-section to the previous layer of the build (i.e. a second layer of the build). Upon photocuring the second layer of the build, the second layer may strongly adhere to the first layer of the build while minimally adhering to the separation membrane 160.

Once the system 100 photocures a second layer of the build, the system 100 can again execute Blocks S120, S130, and S140 to separate the bottom surface of the second layer from the upper surface of the separation membrane 160 and the build window 110. However, in implementations described below, the system 100 can execute variations of Blocks S120, S130, and S140 while separating the second layer of the build when compared to the separation of the first layer based on changes in the geometry of the build (e.g., via the addition of subsequent layers). For example, the system 100 can modify (e.g., reduce or increase) the maximum retraction force, during the retraction phase, based on the addition of new features in a subsequent layer. In another example, the system 100 can modify (e.g., reduce or increase) the target interstitial pressure based on features in a current layer of the build. In yet another example, the system 100 can modify the displacement curve during the retraction phase based on the addition of new features in subsequent layers. In an additional example, the system 100 can modify the advancement speed based on the geometry of subsequent layers.

5.7.3 Print Parameters

In one implementation, the system 100 can adjust or set print parameters for a build based on the resin selected for the build and/or the geometry of the build. For example, if the system 100 receives a resin selection for the build that is characterized by a relatively low green strength and/or a geometry of the build characterized by relatively fine features, the system 100 can broadly reduce the speed of the build and/or the maximum forces allowable at each phase of the build in order to prevent build failure and/or poor dimensional accuracy. In an alternative example, if the system 100 receives a resin selection for the build that is characterized by a relatively high green strength and/or a geometry of the build characterized by relatively robust features, the system 100 can broadly increase the speed of the build and the maximum forces allowable at each phase of the build to increase the speed of the build cycle and therefore decrease manufacturing time.

In one implementation, the system 100 can increase the overlap between phases of the build cycle in response to receiving a more robust build geometry or a resin selection characterized by a high green strength. Thus, the system 100 can: receive a selection of the resin for the build; receive a geometry of the build; and calculate a set of build parameters corresponding to the selection of the resin and the geometry of the build, the build parameters specifying a duration of the pressurization phase, a duration of the retraction phase, a duration of the relamination phase, an overlap between the pressurization phase and the retraction phase, and an overlap between the retraction phase and the relamination phase.

However, the system 100 can modify any aspect of the build process described above in response to particular features present in the geometry of the build and/or the properties (e.g., viscosity and/or green strength) of the resin selected for the build.

5.7.4 Double Separation

In one implementation, the system 100 photocures a single layer in two or more separation stages. Generally, the system 100 can adapt the execution of the method S100 to the particular geometry of the build, even within the same layer. The system 100 can execute two or more stages of the same layer and execute different variations of Blocks S120, S130, and S140 for each stage.

More specifically, the system 100 photocures the first stage of a layer including a first set of layer features and separates the first stage of the layer by executing Blocks S110, S120, S130, and S140. Then, in a second stage, the system 100 instructs the linear actuation system to return the build platform 106 to its initial position in Block S110 before selectively photocuring a second volume of the resin corresponding to a second set of layer features within the same layer. After the system 100 photocures a second set of layer features for the first layer, the system 100 can execute different variations of Blocks S120, S130, and S140 to separate the second stage of the layer. For example, the system 100 can photocure the first set of layer features of the layer and separate the first set of layer features from the separation membrane 160 by executing Blocks S120, S130, and S140; then, to separate the second set of layer features, the system 100 can execute Blocks S130 and S140 (i.e. by instructing the linear actuation system to move the build platform 106 upward without first inflating the interstitial region between the separation membrane 160 and the build window 110). In this example, the system 100 can photocure a first set of layer features and separate using the inflation process of Block S120 and then successively photocure a second more delicate set of layer features by omitting the inflation step of Block S120. However, any of the aforementioned implementations of the method S100 can be executed in succession in different stages of the same layer.

5.7.5 Inter-Layer Feedback

In one implementation, the system 100 can analyze force data recorded at the linear actuation system during the execution of Block S130 for a first layer to calculate changes in the maximum retraction force during the retraction phase, the retraction force/displacement profile, the target interstitial pressure for the pressurization phase, and/or the strength of the vacuum applied during the relamination phase in Blocks S130, S120, and S140 respectively. Additionally, the system 100 can calculate changes to the advancement profile during the advancement phase. Thus, the system 100 analyzes data collected during the execution of a first layer to improve the separation process for a second layer. In one implementation, the system 100 can increase the duration and/or the target interstitial pressure during Block S120 in response to a high peak force recorded during Block S130 during the separation of a previous layer. Additionally or alternatively, the system 100 can reduce the duration and/or the target interstitial pressure during Block S120 in response to a low peak force recorded during Block S130 of a separation of a previous layer.

However, the system 100 can adjust the maximum retraction force applied by the linear actuation system in Block S130, the target interstitial pressure in Block S120, and/or the strength or duration of the vacuum applied in Block S140 in response to force data recorded during separation of a previous layer of the build.

5.7.6 Failure Detection

In one implementation, the system 100 can analyze force data and/or any other data collected during the separation of a previous layer of the build to detect a failure in the separation process. For example, the system 100 can analyze force data recorded during the separation of a previous layer to detect a sudden reduction in applied force at the linear actuation system incongruent with the change in layer geometry corresponding to a failure of the build. Additionally or alternatively, the system 100 can include a camera and can execute optical detection methods utilizing computer vision techniques to corroborate force profile data indicating a build failure. In one implementation, the system 100 can detect a failure in the separation membrane 160 and/or build window 110.

Upon detecting a build failure, the system 100 can notify a user that the build has failed and can recommend changes to the build settings to avoid a failure in a subsequent build attempt.

The systems and methods described herein can be embodied and/or implemented at least in part as a machine configured to receive a computer-readable medium storing computer-readable instructions. The instructions can be executed by computer-executable components integrated with the application, applet, host, server, network, website, communication service, communication interface, hardware/firmware/software elements of a user computer or mobile device, wristband, smartphone, or any suitable combination thereof. Other systems and methods of the embodiment can be embodied and/or implemented at least in part as a machine configured to receive a computer-readable medium storing computer-readable instructions. The instructions can be executed by computer-executable components integrated by computer-executable components integrated with apparatuses and networks of the type described above. The computer-readable medium can be stored on any suitable computer readable media such as RAMs, ROMs, flash memory, EEPROMs, optical devices (CD or DVD), hard drives, floppy drives, or any suitable device. The computer-executable component can be a processor but any suitable dedicated hardware device can (alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the embodiments of the invention without departing from the scope of this invention as defined in the following claims. 

We claim:
 1. A method for additive manufacturing comprising: photocuring a first volume of a resin to form a first layer of a build at a surface of a separation membrane arranged across a build window; measuring a mass of the resin over the separation membrane; calculating a target interstitial pressure based on the mass of the resin; injecting a fluid into an interstitial region between the separation membrane and the build window to the target interstitial pressure to inflate the separation membrane and separate the separation membrane from the build window; subsequent to initiating the injection of the fluid into the interstitial region, retracting the first layer of the build from the build window to peel the separation membrane from the first layer of the build; evacuating the fluid from the interstitial region; and photocuring a second volume of the resin to form a second layer of the build between the surface of the separation membrane and the first layer of the build.
 2. The method of claim 1, wherein injecting the fluid into an interstitial region between the separation membrane and the build window to the target interstitial pressure to inflate the separation membrane and separate the separation membrane from the build window comprises injecting the fluid into the interstitial region between the separation membrane and the build window to the target interstitial pressure to inflate the separation membrane and to overcome a suction force between the separation membrane and the build window.
 3. The method of claim 1, wherein evacuating the fluid from the interstitial region comprises, subsequent to the separation of the separation membrane from the build window and during the retraction of the first layer of the build from the build window, evacuating the fluid from the interstitial region.
 4. A method for additive manufacturing comprising: photocuring a first volume of a resin to form a first layer of a build at a surface of a separation membrane tensioned over a build window; measuring a mass of the resin over the separation membrane; calculating a first pressure based on the mass of the resin; pressurizing an interstitial region between the separation membrane and the build window to the first pressure to inflate the separation membrane and separate the separation membrane from the build window; subsequent to initiating the pressurization of the interstitial region, retracting the first layer of the build from the build window to peel the separation membrane from the first layer of the build; depressurizing the interstitial region to a second pressure; and photocuring a second volume of the resin to form a second layer of the build between the surface of the separation membrane and the first layer of the build.
 5. The method of claim 4: wherein pressurizing the interstitial region to inflate the separation membrane to the first pressure comprises pressurizing the interstitial region to the first pressure to inflate the separation membrane to greater than an ambient air pressure; and wherein depressurizing the interstitial region to the second pressure comprises depressurizing the interstitial region to the second pressure substantially equal to the ambient air pressure.
 6. The method of claim 5, wherein depressurizing the interstitial region to the second pressure is performed via an external air port.
 7. The method of claim 4, further comprising pressurizing a build chamber above the separation membrane to a third pressure greater than the second pressure, the build chamber containing a gaseous environment and the resin.
 8. The method of claim 7, wherein pressurizing the build chamber above the separation membrane to the third pressure comprises pressurizing the build chamber to the third pressure while depressurizing the interstitial region to the second pressure and while retracting the first layer of the build from the build window.
 9. The method of claim 4, wherein photocuring the first volume of the resin to form the first layer of the build at the surface of the separation membrane tensioned over the build window comprises photocuring the first volume of the resin to form the first layer of the build at the surface of the separation membrane tensioned over the build window, the separation membrane laminated over the build window via engagement of a tray assembly comprising the separation membrane and arranged around the build window.
 10. A method for additive manufacturing comprising: photocuring a first volume of a resin to form a first layer of a build adhered to a build platform over a separation membrane arranged across a build window; measuring a mass of the resin over the separation membrane; calculating a target interstitial pressure based on the mass of the resin; injecting a fluid into an interstitial region between the separation membrane and the build window to the target interstitial pressure to inflate the separation membrane and separate the separation membrane from the build window; subsequent to initiating the injection of the fluid into the interstitial region, retracting the build platform and first layer of the build from the build window; evacuating the fluid from the interstitial region; and photocuring a second volume of the resin to form a second layer of the build between the separation membrane and the first layer of the build.
 11. The method of claim 10, wherein retracting the first layer of the build from the build window comprises retracting the first layer of the build from the build window to peel the separation membrane from the first layer of the build.
 12. The method of claim 11, wherein evacuating the fluid from the interstitial region comprises, while retracting the first layer of the build from the build window, evacuating the fluid from the interstitial region to peel the separation membrane from the first layer of the build.
 13. The method of claim 10, further comprising: accessing a target temperature for the resin based on a temperature-viscosity curve and a target viscosity for the resin; and heating the resin to the target temperature.
 14. The method of claim 10, wherein: measuring the mass of the resin over the separation membrane comprises measuring the mass of the resin over the separation membrane based on a measurement of the temperature of the resin and a density of the resin at the measured temperature.
 15. The method of claim 14, further comprising: while injecting the fluid into the interstitial region, measuring a separation distance of the separation membrane from the build window; and adjusting the target interstitial pressure based on the separation distance.
 16. The method of claim 10, wherein retracting the build platform from the build window further comprises: defining a displacement curve based on a target green strength of the resin in a photocured state and a viscosity of the resin in a liquid state; and retracting the build platform according to the displacement curve.
 17. The method of claim 10, wherein retracting the build platform further comprises: calculating a maximum retraction force based on a green strength of the resin in a photocured state and a geometry of the build; measuring a retraction force applied to the first layer of the build during the retraction of the build platform; and adjusting the retraction of the build platform to prevent the measured retraction force from exceeding the maximum retraction force.
 18. The method of claim 17, wherein calculating the maximum retraction force based on a green strength of the resin and the geometry of the build comprises: calculating a maximum stress sustainable by the build based on the geometry of the build; and calculating the maximum retraction force resulting in a stress less than the maximum stress.
 19. The method of claim 10: wherein retracting the build platform and the first layer of the build from the build window comprises retracting the first layer of the build from the build window to a target retraction distance greater than a layer thickness of the build; and wherein photocuring the second volume of the resin further comprises: advancing the first layer of the build toward the build window to a target position above the separation membrane, the target position equal to the layer thickness of the build; and photocuring the second volume of the resin to form the second layer of the build between the separation membrane and the first layer of the build.
 20. The method of claim 19: further comprising accessing a target advancement speed based on a viscosity of the resin and a geometry of the first layer of the build; and wherein advancing the build platform toward the build window to the target position above the separation membrane comprises advancing the build platform toward the build window to the target position at the target advancement speed. 